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Article (refereed) - postprint Tipping, Edward; Chaplow, Jacky S.. 2012 Atmospheric pollution histories of three Cumbrian surface waters. Freshwater Biology, 57 (2). 244-259. 10.1111/j.1365- 2427.2011.02617.x Copyright © 2011 Blackwell Publishing Ltd. This version available http://nora.nerc.ac.uk/16359/ NERC has developed NORA to enable users to access research outputs wholly or partially funded by NERC. Copyright and other rights for material on this site are retained by the rights owners. Users should read the terms and conditions of use of this material at http://nora.nerc.ac.uk/policies.html#access This document is the author’s final manuscript version of the journal article, incorporating any revisions agreed during the peer review process. Some differences between this and the publisher’s version remain. You are advised to consult the publisher’s version if you wish to cite from this article. The definitive version is available at http://onlinelibrary.wiley.com Contact CEH NORA team at [email protected] The NERC and CEH trademarks and logos (‘the Trademarks’) are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Atmospheric pollution histories_SECOND REVISION / Tipping & Chaplow 1 1 Submitted to Freshwater Biology Special Issue on 65 Years of Windermere Research 2 October 2010 3 Revision submitted January 2011 4 5 Atmospheric pollution histories of three Cumbrian surface waters 6 7 E. Tipping & J.S. Chaplow 8 9 Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, 10 Lancaster LA1 4AP, United Kingdom 11 12 13 Correspondence to: Professor Edward Tipping 14 Centre for Ecology and Hydrology 15 Lancaster Environment Centre 16 Bailrigg 17 Lancaster 18 LA1 4AP 19 United Kingdom 20 21 E-mail [email protected] 22 Telephone ++ 44 (0)1524 595866 23 24 25 Keywords: Acidification; Catchment; Heavy metals; Modelling; Weathering 26 Atmospheric pollution histories_SECOND REVISION / Tipping & Chaplow 2 27 Summary 28 1. The CHemistry of the Uplands Model (CHUM), driven by measured and estimated 29 atmospheric deposition, was used to simulate the chemical compositions of three 30 upland Lake District surface waters, Devoke Water (DW), Levers Water (LW) and 31 Mosedale Beck (MB) over several hundred years. 32 2. “Natural acidification” combined with human activities, notably forest clearance, was 33 assumed to have brought about chemically stable acid moorlands by the period 34 1000–1500 A.D. Deposition of sulphur, nitrogen, chlorine and heavy metals, released 35 into the atmosphere by coal-burning and industrial processes, then took place, 36 gradually increasing to maximum levels in the late 20th century. 37 3. Surface water concentrations of chloride are consistent with depositional inputs, 38 whereas the transfer of atmospherically deposited sulphur to the surface waters is 39 delayed by temporary retention processes within the catchment. Over the last 40 40 years, concentrations of pollutant (non-marine) sulphate in the surface waters 41 declined to one-third of their maximum levels. Atmospherically deposited pollutant N 42 continues to accumulate in catchment soils, although a significant fraction appears in 43 surface waters as nitrate. Annual average surface water bicarbonate concentrations 44 were 20 - 60 µmol L-1 in the pristine past, fell nearly to zero in all three waters when 45 acidification was most intense, but now are increasing. 46 4. Combined data from several Lake District upland waters suggest substantial recent 47 increases in concentrations of dissolved organic carbon (DOC). If this can be 48 attributed to acidification reversal, a corresponding decline in DOC concentrations 49 would have occurred as acidification intensified, and pristine surface waters would 50 have been comparatively rich in DOC. 51 5. Major cationic elements enter the soil-water system in deposition (H+, Na, Mg, K, Ca), 52 from organic matter decomposition (H+), or by chemical weathering (Mg, Al, Ca), and 53 are much affected by sorption to soil organic matter (SOM). The surface soils of all 54 three catchments are acid (current pH ~ 4.5) and so variations in surface water 55 chemistry among sites reflect differences in mineral dissolution rates deeper in the 56 soil-rock profile. The simulations indicate pH values of 6.9, 6.1 and 6.4 for DW, LW 57 and MB respectively in the period up to 1800, followed by declines to minima of c. 58 6.0, 4.7 and 5.0 in around 1980, then acidification reversal in agreement with 59 observations. 60 6. The transfer of atmospherically deposited heavy metals to surface waters depends 61 upon their sorption by SOM. Nickel, zinc and cadmium adsorb relatively weakly and Atmospheric pollution histories_SECOND REVISION / Tipping & Chaplow 3 62 therefore are quite readily leached, and sensitive to changes in acidification status. 63 The higher affinities of organic matter to Cu and Pb promote retention and these two 64 metals are continuing to accumulate in soil, despite major declines in deposition over 65 the past several decades. 66 7. The WHAM-FTOX model was used to estimate the maximum number of 67 Ephemeroptera, Plecoptera and Trichoptera species in MB through time, as 68 influenced by chemical variability. The maximum number is estimated to have fallen 69 from 14-15 under pristine conditions to 9-10 when acidification was greatest and a 70 modest recovery to 10-11 species since then. 71 72 Atmospheric pollution histories_SECOND REVISION / Tipping & Chaplow 4 73 Introduction 74 Britain has been affected by atmospheric pollution for a long time (Mannion, 1991; 75 Thorsheim, 2006). Coal burning already took place on a significant scale in the 17th century, 76 adding sulphur, nitrogen and metals to the atmosphere, while the mining and smelting of 77 metal ores, especially of lead, was also widespread. Emissions increased during the 78 Industrial Revolution of the 18th and 19th centuries, and into the 20th century. To the effects 79 from power generation and manufacturing industry were added those of transport and 80 intensifying agriculture, especially with respect to nitrogen (Sutton et al., 2008). The effects 81 of pollutants were localised at first, but then spread to more remote areas. Thus the English 82 Lake District has been subjected to various forms of atmospheric pollution for several 83 centuries, and has also contributed through its own mining activities (Cameron, 2000). Direct 84 evidence for the long-term deposition of pollutants to the area comes from lake sediment 85 records showing the increasing deposition of metals until the latter part of the 20th century 86 (Hamilton-Taylor, 1979; Ochsenbein et al., 1983; Yang & Rose, 2005). More recent 87 pollutants include radionuclides, notably caesium-137, due to atmospheric weapons testing 88 and reactor accidents (Beresford et al., 1992), and organic contaminants such as 89 polychlorinated biphenyls and polycyclic aromatic hydrocarbons (Gevao et al., 2000). 90 Monitoring and process studies of atmospheric pollutant deposition and its effects go back to 91 the 1950s, and the work of E. Gorham (1955, 1958), who described rain composition at 92 various sites, relating it to sources and pointing out the high acidity of rain. Extensive 93 monitoring and analytical work during the 1970s and 1980s, led by D.W.Sutcliffe, 94 documented spatial and temporal variation in the chemistry of Lake District surface waters 95 and rainfall (Carrick & Sutcliffe, 1982, 1983; Sutcliffe & Carrick, 1983, 1988; Sutcliffe et al., 96 1982). Spatial variations in surface waters were studied by Thornton & Dise (1998). 97 Continuation of temporal monitoring demonstrated the reversal of surface water acidification, 98 attributed to declines in sulphur deposition (Tipping et al., 1998, 2000); this was one of the 99 first documented occurrences of such reversal, reflecting the responsiveness of Lake District 100 catchments. Monitoring of two small lakes is now also performed by the UK Acid Waters 101 Monitoring Network (Monteith & Evans, 2005). 102 As well as being useful in themselves, to delineate changes and spatial differences, the 103 monitoring programmes provide data for the running and testing of simulation models, which 104 by quantitatively relating depositional inputs to surface water composition, permit the testing 105 of hypotheses about catchment processes that generate surface waters. Simple modelling 106 of water chemistry in terms of deposition and soil-rock processes, sorption and weathering 107 was performed by Tipping (1989, 1990). The MAGIC acidification model has also been 108 applied both to specific Lake District sites (Whitehead et al., 1997) and as part of regional- Atmospheric pollution histories_SECOND REVISION / Tipping & Chaplow 5 109 scale analyses (Evans et al., 1998). The more comprehensive biogeochemical model CHUM 110 has been used to explore acidification (Tipping et al., 2006a), heavy metals (Tipping et al., 111 2006b) and radionuclides (Tipping, 1996). The behaviour of radiocaesium derived from 112 Chernobyl has also been studied by modelling (Smith et al., 1995). 113 In the present paper, we report new applications of the CHUM model, which takes into 114 account deposition compositions and amounts, soil chemistry, chemical weathering, and 115 relevant parts of the C, N and S cycles. We focus on three catchments that receive little or 116 no direct input of chemicals such as fertilisers, so any contamination comes from the 117 atmosphere as wet and dry deposition. We apply and test assumptions about the 118 combination of biogeochemical and hydrological processes that determine element retention 119 and transport within the catchments. To calibrate and assess the model, we use stream and 120 lake chemistry monitoring data starting in the 1970s, and in a few cases even earlier, making 121 a record of 40 years or more. The main aim is to explain how several centuries of pollution 122 by atmospheric deposition have affected the catchments, starting from the near-pristine 123 conditions that we assume prevailed in the middle of the last millennium, and arriving at the 124 present day.